Weird, I don't notice any difference between winter and summer driving in my MPG. I'm in eastern Wa state, close to Id. I stay around 16.5 mpg normal driving, around the same for city and 19 for open highway on the 3 to 4 hour drive between here and Seattle.

The only thing that really effects me is the strong winds we get but, that normally only effects my Seattle trips.

 

throw some lucas upper cylinder in there too and you'll really see better numbers

 

At WOT only. Anything other than WOT and it will maintain 14.7:1 quite religiously.